Integrated physicochemical and microbial analyses reveal redox-driven microbial community structure in a polycyclic aromatic hydrocarbon–polluted subsurface

Hydrocarbon-polluted sites are a global environmental concern. Although bioremediation is a cost-effective and sustainable remediation method, its efficiency is often impaired by various environmental and microbial factors. Further advancements in bioremediation require a deeper understanding of the relationship between the soil microbiome and the physicochemical parameters that limit biodegradation. Here, we investigated a 3-m-deep polycyclic aromatic hydrocarbon (PAH)-polluted soil core from a historically polluted site in The Netherlands. Soil samples were taken from six depths at 50 cm intervals, followed by a physicochemical characterisation, including measurements of PAH, electron acceptors, pH and electrical conductivity. These analyses were complemented by a detailed microbial community analysis. Our findings suggest that microbial communities are primarily shaped by a combination of the availability of electron acceptors and pollution levels. Additionally, groundwater level fluctuations appear to play an important role in the transport and replenishment of electron acceptors. In-depth community analysis further revealed a diversity of metabolic strategies employed by the different communities to cope with the oversupply of electrons. Collectively, these results demonstrate that microbial communities in PAH-polluted soils vary according to habitat-specific redox environments. Therefore, microbial community analysis can serve as an additional diagnostic tool to infer the specific physicochemical constraints that limit efficient biodegradation. Our findings provide a detailed, integrated interpretation of physicochemical and microbial field data, offering insight into the heterogeneous nature of in situ biodegradation. They further highlight the value of comprehensive and integrated microbial community and physicochemical analyses in identifying biodegradation-limiting factors in the field.